1. Field of the Invention
The present invention relates to a fuel supply control system for an internal combustion engine, and particularly, to a control system that corrects an amount of supplied fuel according to an operating condition of the internal combustion engine.
2. Description of the Related Art
An example of a fuel supply control system for an internal combustion engine is disclosed in Japanese Patent Laid Open Sho 60-13932. The known fuel supply control system controls a fuel supply to an internal combustion engine whose operation can be switched between a partial-cylinder operation, wherein operation of some of the cylinders is halted, and an all-cylinder operation, wherein all of the cylinders are operated. According to the known fuel supply control system, when engine operation shifts from the partial-cylinder operation to the all-cylinder operation, fuel is supplied to the cylinders that are halted during the partial-cylinder operation by an amount greater than the amount of fuel supplied to the cylinders that are operated during the partial-cylinder operation for a predetermined period of time.
According to the conventional fuel supply control system, it is possible to prevent the operating performance (combustion state) of the engine from deteriorating due to a reduction in temperature of the cylinders that are not operating during the partial cylinder operation when the all-cylinder operation is restarted.
Exhaust valves of operating cylinders in an internal combustion engine are exposed to hot exhaust gases, while the exhaust valves of halted or non-operating cylinders are not exposed to such hot exhaust gases. Accordingly, it is confirmed that a lift amount of the exhaust valve slightly changes depending on whether the cylinder is operating or halted due to the thermal expansion or contraction of the valve body of the exhaust valve. Further, when the exhaust valve is opened, a part of the hot exhaust gases may return to the combustion chamber. If the lift amount of the exhaust valve changes, the amount of returning exhaust gases changes.
In the conventional fuel supply control system described above, the change in the lift amount of the exhaust valve is not taken into consideration. Accordingly, the incremental amount of fuel supplied to the halted cylinders during the partial-cylinder operation may be incorrect, which makes an air-fuel ratio of the air-fuel mixture in the combustion chamber deviate from a desired value and the exhaust characteristic of the engine is ultimately degraded.
In a further example, wherein the fuel supply to the operating cylinders is interrupted during the partial-cylinder operation, the lift amount of each exhaust valve slightly changes immediately after the supply of fuel is restarted. Therefore, the air-fuel ratio deviation may occur in the operating cylinders during the partial-cylinder operation.